How do I find a p value given the Z statistic using the empirical rule?
https://www.khanacademy.org/math/probability/statistics-inferential/normal_distribution/v/ck12-org-normal-distribution-problems-empirical-rule
but if you really want the right answer to a specific problem without fooling around with
68 - 95 - 99.7
use
http://davidmlane.com/hyperstat/z_table.html